1. Field of the Invention
The present invention relates to an altitude measurement apparatus of a vertical takeoff and landing (VTOL) aircraft, and more particularly, to an altitude measurement apparatus that may easily calculate an altitude of a VTOL aircraft without using an expensive equipment such as a separate altimeter.
2. Description of the Related Art
A conventional altitude measurement scheme may measure an altitude using reception data of a Global Positioning System (GPS), a pressure altitude sensor, electromagnetic waves, and the like.
In the case of using the GPS, altitude information may be provided. However, when the GPS does not correspond to an expensive GPS receiver, or when the altitude is low, a great error may occur. In addition, in dynamic environments, the error range may increase and a number of visible satellites may be limited. As technology to complete the above disadvantages and to enhance accuracy, a Differential Global Positioning System (DGPS) may be employed. In this case, since a GPS base station needs to be separately installed and a predetermined range with the GPS base station is limited, the DGPS may be spatially limited.
In the case of using the pressure altitude sensor, the pressure altitude sensor is very sensitive to an external environment and noise. Consequently, since variation of data is great and an error frequently occurs in a low altitude, a reliability issue may occur. In addition, the atmospheric pressure frequently varies depending on surrounding environments such as a region, a temperature, wind, and the like. Accordingly, when the pressure altitude sensor is used alone, the error range may generally be greater than or equal to ±10 m and thus it is very difficult to accurately measure the altitude.
When the altitude is measured using a radio altimeter that is generally used for a near distance, the altitude may be accurately calculated by calculating a distance based on a time used to emit radar waves and to receive returned radar waves. However, the radio altimeter is one of to expensive equipments. Accordingly, attempts have been made to enhance the accuracy and save costs in measuring the altitude.